NetNews Usenet Archive 1992 #31/NN_1992_31.iso/spool/comp/lang/c/19067

Text File | 1992-12-31 | 2.0 KB | 52 lines

Newsgroups: comp.lang.c
Path: sparky!uunet!uunet.ca!canrem!telly!druid!darcy
From: [e-mail] (D'Arcy J.M. Cain)
Subject: Re: Arrays with variable dimensions?
Message-ID: <[e-mail]>
Date: Thu, 31 Dec 1992 10:46:44 GMT
References: <[e-mail]> <[e-mail]>
Organization: D'Arcy Cain Consulting
Lines: 41

[e-mail] (Bernard Farrell) writes:
>[e-mail] (John B. Lee) writes:
>: Is it possible to create an array that would change size according
>: to user input?
>float fl_arr[] = NULL;   /*  This is actually a float * -- no space  */

You didn't even try this did you?  This actually does assign space to an
array.  I don't know what your compiler does with the "= NULL" but assuming
it even accepts it (mine doesn't) it certainly doesn't do what you think it
does.  If you want a float * why didn't you just declare that:

float *fl_arr = NULL;

I would do the rest slightly different than your example but with the above
change your code should work.

>This allows the array to increase in size as required.  The
>alternative is to do a malloc(), instead of using realloc(),
>based on a value given at run-time.   Note that the above
>code works only when realloc() works as malloc() when the
>first parameter is NULL -- some implementations of realloc()
>do not have this behavior.

If you can count on an ANSI compiler you are fine but using a malloc first
is safer if you can't be sure.  Perhaps something like this at the start
of the code:

#ifndef    __STDC__
  if ((fl_arr = malloc(sizeof(*fl_arr) * ARRAY_INCR)) == NULL)
    print_horrible_error_and_exit();
  fl_max = ARRAY_INCR;
#endif

Of course if you are really paranoid about the __STDC__ constant you'll
just do this every time regardless.

--
D'Arcy J.M. Cain ([e-mail])  |
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